Dynamic dimming led backlight

ABSTRACT

Disclosed herein is a system for controlling the interactions of light between adjacent subsections of a dynamic LED backlight. Preferred embodiments contain a dividing wall positioned between each adjacent subsection of the LED backlight. The dividing wall may be in contact with the LED backlight and extend away from the LED backlight. The dividing wall may prohibit light from a first subsection from entering an adjacent second subsection at its full luminance. The luminance for each adjacent subsection may be approximately half of the full luminance of each subsection, when measured at the location of the dividing wall.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims priority to U.S.application Ser. No. 13/722,537 filed on Dec. 20, 2012, which is in turna divisional of and claimed priority to U.S. application Ser. No.12/793,474 filed on Jun. 3, 2010, now U.S. Pat. No. 8,350,799, each ofwhich are herein incorporated by reference in their entirety.

TECHNICAL FIELD

Disclosed embodiments relate generally to an LED backlight havingindividually controlled subsections and an associated liquid crystaldisplay.

BACKGROUND OF THE ART

Liquid Crystal Displays (LCDs) contain several layers which work incombination to create a viewable image. A backlight is used to generatethe rays of light that pass through what is commonly referred to as theLCD stack, which typically contains several layers that perform eitherbasic or enhanced functions. The most fundamental layer within the LCDstack is the liquid crystal material, which may be actively configuredin response to an applied voltage in order to pass or block a certainamount of light which is originating from the backlight. The layer ofliquid crystal material is divided into many small regions which aretypically referred to as pixels. For full-color displays these pixelsare typically further divided into independently-controllable regions ofred, green and blue subpixels, where the red subpixel has a red colorfilter, blue subpixel has a blue color filter, and green subpixel has agreen color filter. These three colors are typically called the primarycolors. Of course, some displays may use additional color filters (suchas adding a yellow filter) and these could also be used with theembodiments herein.

The light which is passing through each subpixel originates as “white”(or broadband) light from the backlight, although in general this lightis far from being uniform across the visible spectrum. The subpixelcolor filters allow each subpixel to transmit a certain amount of eachcolor (red, green or blue). When viewed from a distance, the threesubpixels appear as one composite pixel and by electrically controllingthe amount of light which passes for each subpixel color the compositepixel can produce a very wide range of different colors due to theeffective mixing of light from the red, green, and blue subpixels.

Currently, the common illumination source for LCD backlight assembliesis fluorescent tubes, but the industry is moving toward light emittingdiodes (LEDs). Environmental concerns, small space requirements, lowerenergy consumption, and long lifetime are some of the reasons that theLCD industry is beginning the widespread usage of LEDs for backlights.

LCDs are becoming popular for not only home entertainment purposes, butare now being used as informational/advertising displays in both indoorand outdoor locations. When used for information/advertising purposes,the displays may remain ‘on’ for extended periods of time and thus wouldsee much more use than a traditional home theatre use. Further, whendisplays are used in areas where the ambient light level is fairly high(especially outdoors) the displays must be very bright in order tomaintain adequate picture brightness. When used for extended periods oftime and/or outdoors, overall energy consumption can become an issue.Thus, it is desirable to limit the power consumption of these displaysas much as possible while maintaining image fidelity.

SUMMARY

Exemplary embodiments provide a backlight with individually controlledsubsections. The luminance for each subsection can be controlled basedon the image data being sent to the LCD. The incoming image data may beanalyzed to determine the requirements for each subsection, and some maybe selectively ‘dimmed’ if they correspond to portions of the imagewhich do not require the full luminance output of the backlight.Selectively dimming portions of the backlight allows for severalbenefits, including but not limited to reduced power consumption, longerproduct lifetime, and higher contrast ratios.

These and other objects are achieved by a device as described in thefollowing detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding will be obtained from a reading of the followingdetailed description and the accompanying drawings wherein identicalreference characters refer to identical parts and in which:

FIG. 1 is a front view of a backlight with individually controlledsubsections;

FIG. 2 is a front view of LCD image data where the image is divided intoseveral subimages;

FIG. 3 is a histogram of a subimage;

FIG. 4 is a flow chart for one embodiment for analyzing the subimagehistogram data;

FIG. 5 is a front view of the backlight where each subsection is beingdriven at the appropriate luminance level based off the histogram datafor the corresponding subimage;

FIG. 6 is a front view of the re-scaled LCD image data;

FIG. 7 is a front view of the backlight from FIG. 4 after diffusion;

FIG. 8 is the image resulting from combining the diffuse backlight ofFIG. 7 with the rescaled LCD image of FIG. 6;

FIG. 9 a surface plot of a fully illuminated subsection of the backlightthat has been convolved with a Gaussian filter;

FIG. 10 is a plot of relative luminance versus physical position on apair of adjacent subsections when using the virtual subsection method;

FIG. 11 is a perspective view of one embodiment for controlling the‘bleeding’ of light between adjacent subsections of the backlight;

FIG. 12 is a plot of relative luminance versus physical position onsubsections when using pre-determined brightness profiles; and

FIG. 13 is a schematic view of one embodiment for the physicalarchitecture of controlling the dynamic backlight.

DETAILED DESCRIPTION

FIG. 1 shows a backlight 10 which has been divided into severalindividually-controllable subsections 15. The backlight 10 produceslight through a plurality of LEDs (not shown) which are mounted to thefront face of the backlight 10. In this example, an 8×8 array ofsubsections 15 is shown. However, any number, shape, and size ofsubsections may be used with the various embodiments. The number ofactual subsections may depend upon: the size of the display, cost,complexity of controlling circuitry desired, and desire for maximumpower savings. Ideally, the greater number of subsections will provide ahigher level of control and performance by the system. It should benoted that lines 16 are only used to represent the divisions regardingcontrol of the subsections 15 and are not required as actual lines orphysical divisions of the backlight 10.

FIG. 2 provides the LCD image data 20, where this image is divided intosubimages 22 which correspond with the subsections 15 of the backlight10 (shown in FIG. 1). Again, the lines 26 are only used to represent thedivisions of the subimages and are not physical divisions of the LCD andshould not be visible through the LCD assembly.

FIG. 3 shows a plot of histogram data for one of the subimages 22 shownin FIG. 2. The brightness index value is shown along the x-axis and thenumber of pixels within the subimage which have the correspondingbrightness index value is shown along the y-axis. Here, the brightnessindex values range from 0 (no saturation) to 255 (fully saturated).Three separate plots are shown in FIG. 3: red subpixels 37, bluesubpixels 30, and green subpixels 35. It can be observed from this plotthat the red subpixels will control the brightness requirements for thesubsection of the backlight as the red subpixel histogram data is skewedto the right of the green 35 and blue 30 data. Further, it can also beobserved that the blue data 30 is bimodal, meaning that there are twopeaks in the data, a first one 31 near zero and a second one 32 near 60.This bimodal characteristic will be discussed further below.

The histogram data for each subimage is analyzed to determine the properluminance level for the backlight subsection corresponding to eachsubimage. FIG. 4 shows one embodiment for analyzing the histogram datafor each channel (in this example: red, green, and blue) to determinethe proper luminance setting for the backlight subsection.

Once the histogram data has been created 40, a first average μ₁ andstandard deviation σ₁ are calculated 41. The following is one method forcalculating these values and analyzing them:

Let N=the total number of pixels (red, green, or blue) in the subimage.

Denote the histogram as H(i) where i ranges from 0 to 255

Calculate the average from:

$\mu_{1} = {\frac{1}{N}{\sum\limits_{i = 0}^{255}{i \cdot {H(i)}}}}$

Calculate Standard Deviation

$\sigma_{1} = \sqrt{{\frac{1}{N}\left( {\sum\limits_{i = 0}^{255}{{H(i)} \cdot i^{2}}} \right)} - \mu_{1}^{2}}$

The initial luminance value for this subsection of the backlight maythen be calculated 42 as the average value plus one and a half standarddeviations. Y=μ₁+1.5·σ₁. It should be noted that one and a half standarddeviations was chosen as effective for one embodiment. Depending onseveral factors, some systems may require more or less than 1.5 standarddeviations for adequate system performance. This variable could beadjusted for each display.

The backlight luminance can range from ‘off’ to ‘full on’ and thesepoints, along with all of the settings in between, should be calibratedwith the brightness index values from the histogram which can also varyfrom 0 (off) to 255 (full on). Thus, once the initial luminance value iscalculated it may be compared with the maximum value of 255 (see step43). If the initial luminance value is greater than 255, then thebacklight luminance for this subsection is simply set to full on (255)and is stored for this channel (go directly from step 43 to step 47).The use of ‘channel’ herein denotes one of the primary colors that areused to create the image within the LCD. As discussed above, a typicalLCD contains three channels (Red, Green, and Blue) but other LCD designsmay use additional colors (such as Yellow) and thus may contain 4 ormore channels.

Next, the histogram data for this channel may be tested for a bimodaldistribution 44. This step may be performed because if the distributioncontains multiple peaks, simply averaging and adding some amount ofstandard deviations may completely miss a peak which would require ahigher backlight level. For example, in reference to FIG. 3, asmentioned above, the blue curve 30 may be considered bimodal. Theinitial luminance Y_(i) for the blue curve 30 may fall somewhere inbetween peaks 31 and 32, thus missing the peak 32 which requires thehighest amount of backlight (i.e. if the blue curve were driving thebacklight level, the minimum luminance level would have to be closer to70, to ensure that peak 32 achieves its necessary illumination). In thisparticular case however, it would not affect the outcome of the analysisbecause the highest luminance value between the three channels is thevalue which will be finally used for the subsection (see step 48 in FIG.4). However, the test for bimodal distribution may still be performed toensure that the driving color (in this particular case the red channelis actually the driving color) does not contain several peaks such thatone would not be adequately illuminated.

The following is one method for determining if a histogram is bimodal44. Using Otsu's algorithm, find the optimal separation point betweendistributions in the histogram:

C=nB(T)nO(T)[μB(T)−μO(T)] (Otsu's algorithm)

-   -   where:    -   Tis the threshold value and ranges from 0 to 255    -   nB(T) is the number of pixels that fall below the threshold        value    -   nO(T) is the number of pixels that fall above the threshold        value    -   μB(T) is the average value of the pixels below the threshold        value    -   μO(T) is the average value of the pixels above the threshold        value    -   Perform Otsu's algorithm for each for each value of T in the        histogram and determine the T which corresponds to the maximum        value of C (this will be referred to as T_(max) also known as        the Otsu Threshold).    -   Compare T_(max) to the first average value μ₁.    -   If, |T_(max)−μ₁|≦Δ, then the histogram data is not bimodal and        the luminance value for the subsection is equal to the initial        luminance value. Y_(f)=Y_(i)    -   Note, Δ may be selected for each display setup and may need to        be adjusted depending on the type of display and what is being        shown on the display. Acceptable results have been found for        some displays with a Δ value near 10.    -   If, ⊕T_(max)−μ₁|>Δ, then the histogram data is bimodal and the        following steps should be performed:        -   Calculate a second average and a second standard deviation            based on the histogram data to the right of the Otsu            Threshold T_(max). (see step 45 in FIG. 4)        -   Set j=T_(max).

$N = {\sum\limits_{i = {j + 1}}^{255}{H(i)}}$

-   -   -   // Set N to new sample size        -   Calculate the Second average from:

$\mu_{2} = {\frac{1}{N}{\sum\limits_{i = {j + 1}}^{255}{i \cdot {H(i)}}}}$

-   -   -   Calculate the Second Standard Deviation from:

$\sigma_{2} = \sqrt{{\frac{1}{N}\left( {\sum\limits_{i = {j + 1}}^{255}{{H(i)} \cdot i^{2}}} \right)} - \mu_{2}^{2}}$

The final luminance value (Y_(f)) for this channel can then becalculated 46 as the average plus one standard deviation.Y_(f)=μ₂+1.0·σ₂ Again, acceptable results have been found by using onestandard deviation, but different display setups may require a differentnumber of standard deviations. This final luminance value should becompared to the maximum luminance value possible (255) and if it islarger than this value, the luminance value will simply be stored as themaximum luminance of 255. (If Y_(f)>255 then Y_(f)=255) The finalluminance value for this channel is then stored 47 and steps 40-47 arerepeated for the remaining two channels. Finally, when the finalluminance value for all three channels (R, G, and B) has beendetermined, they are compared with one another and the largest finalluminance value Y_(f) is stored 48 as the proper luminance value for thebacklight subsection.

FIG. 5 shows what the backlight 10 may look like once each of theluminance values has been stored and the corresponding subsections aredriven at their proper luminance values (after Gamma correction has beenperformed, if necessary—see below for more information on Gammacorrection). This may involve a conversion of the luminance values tocurrent/voltage levels and can easily be accomplished by one skilled inthe art by creating a linear relationship where luminance level 0corresponds with 0 amps (or volts) and luminance level 255 correspondsto x amps (or volts), where x represents the power level that generatesthe maximum luminance from the LEDs). It can be easily observed fromFIG. 5 that some subsections are completely on (white) while others areslightly gray to dark grey. The capability of dimming these sections ofthe backlight will save power as well as provide a deeper black/darkcolor since the backlight is not shining through the liquid crystalmaterial at full luminance.

However, LCD subpixel voltages are typically determined based on a ‘fullon’ backlight and when sections of the backlight are dimmed, thesubpixel voltages may need rescaled (‘adjusted’) to ensure that thepicture fidelity remains high and the proper colors are produced by thedisplay. One method for rescaling the LCD subpixel voltages is to dividethe subpixel voltage by the ratio of proper luminance level to maximumluminance. FIG. 6 shows the resulting LCD image data (without theadjusted backlight levels) once it has been rescaled based on thecalculated backlight luminance levels.

For example, subsection 50 shown in FIG. 5 may have a luminance level of128. This would be 128 out of a possible 255 (maximum luminance),resulting in 128/255=approximately ½. As an illustration, assume thatone of the subpixel voltages for subsection 50 was originally 1 mV. Torescale this subpixel voltage, divide 1 mV by ½. Now, the subpixelvoltage should be 2 mV. Assuming that we are dealing with a normallyblack LCD stack (voltage is required to orient the crystals to passlight) this increase in subpixel voltages is required because we havedecreased the backlight level. Thus, from FIG. 5 we know that thebacklight will decrease approx. 50% at subsection 50, so in order tocreate the original colors in the image, the subpixel voltage must beincreased in order to allow more light through the liquid crystals. Theseemingly brighter resulting LCD image for subsection 50 can be observedin FIG. 6. Note, that FIG. 6 only shows the image data and does not takeinto account the actual backlight levels that are illuminating the LCD,so although subsection 50 appears lighter, this will be accounted foronce the new backlight levels are applied.

As a second example, subsection 55 shown in FIG. 5 may have a luminancelevel of 255 (maximum luminance). This would be 255/255, or 1. Thus,assuming any original subpixel voltage for subsection 55, say V, theresulting scaled subpixel voltage would be identical because thebacklight subsection remains at full on. V/1=V. This can be observed inFIG. 5 as the subsection 55 appears white. Also notice that subsection55 in FIG. 6, appears identical to the original image in FIG. 2 becausethe backlight remains at ‘full on’ so the subpixel voltages have notbeen altered from their original settings.

It is common in LCD assemblies to place a light diffusing/scatteringelement (herein ‘diffuser’) in between the backlight and the liquidcrystal material in order to provide a more uniform appearance of lightthrough the display. Without the diffuser, the LED point-sources oflight may be visible through the final display. Thus, when the backlightfrom FIG. 5 is placed behind a diffuser, the resulting luminance patterncan be seen in FIG. 7. Further, when the diffused backlight from FIG. 7is placed behind the rescaled LCD image data from FIG. 6, the resultingimage from the LCD is shown in FIG. 8.

As can be easily observed, the diffusing properties alter the actualluminance levels of the backlight, especially near the edges of thesubsections. Looking at subsection 50 for example, the luminance in thecenter 51 is acceptable, while the luminance near the edges 52 has beenincreased due to ‘bleed over’ from brighter adjacent subsections 60.

One method discovered to account for this phenomenon is the creation ofa ‘virtual backlight’ or ‘VB’ where the ‘bleed over’ behavior ofadjacent subsections can be mathematically modeled and accounted forduring the rescaling of the LCD subpixel voltages. There are manymethods for mathematically modeling a given backlight in order to createa VB.

One method for creating the VB may be referred to as ‘virtualsubsections’ and is based on the use of a stored matrix of data thatrepresents the appearance of a single, fully illuminated subsection inthe backlight assembly as seen through the diffuser. FIG. 9 provides asurface plot of a fully illuminated subsection 90 that has beenconvolved with a Gaussian filter. The subsection 90 has a width (W) 93,height (H) 92, and a tail (T) 95, where W, H, and T are each measured inpixels. The tail 95 represents the subpixels which may be impacted bythe luminance from adjacent subsections of the backlight. In otherwords, illumination of the subsection that extends beyond the physicaledge of the subsection 90. Thus, the dimensions of the stored matrix forthe subsection would be (2T+W)×(2T+H). Because the virtual subsection islarger than the actual subsection, the adjacent subsections may beoverlapped and the principle of additive light may be used to blend theedges of the subsections.

FIG. 10 illustrates the relative luminance versus physical position on apair of adjacent subsections. The x-axis of this figure represents thepixel location while the y-axis represents the relative luminance of thebacklight subsections. Relative luminance refers to the percentage ofthe backlight luminance Y, which was determined for the subsection(subsection) in FIG. 4. Thus, 0.5 would represent one-half of theluminance, 0.25 would represent one-quarter of the luminance, etc. Theplot for a first subsection 100 and an adjacent second subsection 101are shown. The line 105 represents the physical dividing line betweenthe subsections. Looking at the first subsection 100, at pixel zero thefull luminance level is recorded. The relative luminance decreases asthe pixel location increases (as we approach the division between thesubsections 105). At pixel 90, only half of the full luminance level isrecorded. As the pixel location continues to increase (as we move awayfrom the division between the subsections 105) the relative luminancecontinues to decrease until it reaches zero at pixel 180. Thus, for thisexample the tail T, of each subsection may be 90 pixels long. Asymmetrically-opposite trend can be seen with the plot for the adjacentsubsection 101.

It should be noted that because the plot for the adjacent subsections100 and 101 are symmetrical about line 105 and about the relativeluminance of 0.5, if the subsections were driven to the same backlightluminance level they would blend to create 100% luminance across theline 105 between the subsections. Obviously, at line 105 the VB data foreach subsection is at 0.5 or 50% of the backlight luminance for thatsubsection, so if each subsection were driven to the same backlightluminance, these would add together to create the same luminance levelacross the line 105. If the subsections were driven to differentluminance levels, as the VB data is entered, this will blend between thedifferent luminance levels. For example, at pixel location 38 withinsubsection 100, the VB data should be 90% of the luminance forsubsection 100 plus 10% of the luminance for subsection 101.

Obviously, the relationship shown in FIG. 10 is only applied to adjacentsubsection edges and to subpixels which are within the ‘tail’ portion ofthe adjacent subsections. Thus, subsection edges which are not adjacentto any other subsections (i.e. along the perimeter of the overalldisplay) may not show this relationship and may simply use 100% of theluminance level as the VB data for that subsection.

By using the luminance values for each backlight subsection along withthe model for backlight luminance along the subsection edges, an arrayof VB data for each subsection can be stored and then combined to createa larger array which contains VB data for each pixel in the display. Asdiscussed above, the original subpixel voltages may then be divided bythe ratio of VB data over the maximum backlight value in order toproperly rescale the original LCD image data.

It should be noted that although a Gaussian curve has been used in FIG.10 to represent the relationship between adjacent subsections, this isnot required. For some embodiments a linear relationship or exponentialfunction may provide a more appropriate mathematical representation ofwhat is actually occurring with the diffused backlight. Othermathematical models are discussed below. This brings up an interestingpoint to keep in mind when designing this type of system. Either amathematical system can be derived to model the existing physicalbacklight or the physical backlight may be designed so that it performssimilar to a selected mathematical model.

If using the gaussian relationship shown in FIG. 10, it may beadvantageous to design the physical system such that this type ofrelationship actually exists. For example, the backlight and diffusershould be designed such that only 50% luminance exists at theoverlapping edge of each subsection. FIG. 11 shows one method foraccomplishing this specific embodiment, where an array of dividing walls120 has been used between the backlight LEDs 125 and the diffusingelement (not shown). FIG. 11 shows a simplified figure as only a 3×3array is shown and the figure does not show LEDs in every subsection.However, as discussed above, the number of backlight subsections canvary depending on many different factors, and one skilled in the art caneasily modify the simplified FIG. 11 into an 8×8 array (or any otherarrangement) with LEDs in every subsection.

Preferably, there would be a gap between the end of the dividing walls120 and the diffuser. This would prevent any of the dividing walls 120from being visible through the final display. The precise geometry ofthe dividing walls 120 and their relationship to the diffuser mayrequire fine tuning for each display. Acceptable results have been foundfor 70 inch LCD displays where the dividing walls 120 are about two tothree inches high with a gap between the dividing wall 120 and diffuserof 30-40 mm.

As mentioned above, other mathematical models may be used to simulatethe backlight through the diffuser. One other method is to use a pointspread function (PSF). If the diffuser is treated like an optical lowpass filter, then a 2D filter operation can be performed on the virtualbacklight. One could also modify the PSF by observing that a diffusedbacklight only requires a blurring operation along the boundariesbetween subsections.

An examination of the edges between a fully illuminated subsection andan adjacent dimmer subsection constructed via the Gaussian Point SpreadFunction reveals a series of common curves. FIG. 12 shows the change inrelative illumination from 1 to 0.5 (curve 130), 1 to 0.25 (curve 132),and 1 to 0 (curve 134). If we denote Z(x) as the curve that goes from 1to zero, then it is possible to recreate any change in brightnessbetween adjoining subsections with the equation: f(x)=y₁+Z(x)·(y₀−y₁)where y₀ is the brightness of the starting subsection and y₁ is thebrightness of the ending subsection.

Thus, a two-step process for this method could include: (1) Create aseries of changing brightness lines that run vertically down the middleof each subsection using the above formula. If the subsections arerectangular, then a “longer” brightness function will be required forthis operation and (2) Starting at the top of the VB, create a series ofhorizontal brightness curves using the data from step 1 as the endpointsfor each curve.

A final technique to produce a virtual backlight would be through theuse of Bezier Curves. In this approach, cubic splines could be used tointerpolate between the subsection centers and thus simulate diffusion.For each point in the Virtual Backlight, the following equation would becalculated:

B(t)=(1−t)³ P ₀ ⁻3t(1−t)² P ₁+3t ²(1−t)P ₂ +t ³ P ₃ , tε[0,1]

As discussed above, once the data for the VB has been generated, it maybe divided into the corresponding subpixel voltages in order to properlyrescale the LCD video image. This can be accomplished in many ways.Because division is typically a time-consuming operation, one exemplaryembodiment may use a 256 byte lookup table of 8-bit scaling factors.These would be multiplied by each pixel and then followed by an 8-bitshift. The 8-bit shift can be skipped if only the upper byte of theproduct is used. If an overflow occurs, the resulting pixel value wouldbe 255.

Before driving the backlight subsections with the appropriate luminancevalues, gamma correction may be applied. This step may help correct thecontrast and may also provide additional power savings. Assumingbacklight intensities from 0 to 255, one method of gamma correction maybe: I=255·(Y/255)^(v) where γ is typically equal to 2.2 (but this may bevaried depending on the application). For example, assume that theluminance value (Y) for the subsection was calculated to be 128. Whenthis value is used in the gamma equation above, the actual intensity ofthe backlight (I) is calculated to be 56. This backlight intensity (I)can now be converted to actual voltage/current and sent to theappropriate backlight subsection. Also, the re-scaled image data can nowbe sent to the LCD as the backlight is updated.

An example for the physical architecture which could perform theoperations as discussed above is now presented. It should be pointed outthat this architecture is only an example and those skilled in the artcould modify this example or create other types of physical architecturewhich are capable of performing the operations discussed herein.

FIG. 13 shows a schematic representation of one example for the physicalarchitecture. This specific example assumes the following: the input isRGB data on a 24-bit wide data bus, an 8×8 backlight array is used, theoutput is RGB data on a 24-bit wide data bus, an external pixel clock isavailable, the maximum LCD resolution is 1080 by 1920 for a total of2,073,600 pixels, the Samsung LTI700HD01 is the assumed LCD, the designshould support a pixel clock of 148.5 Mhz.

Two frame buffers 200 may be used to store the incoming frame andprocess and output the outgoing frame. Each frame buffer should store2,073,600 RGB values and the width of the frame buffer should be atleast 24 bits. Eight, three channel histogram accumulators 210 may beused for statistical processing. Each accumulator 210 should consist of256 15-bit counters. There may be accumulators for each of the threecolor channels (if using an RGB-type LCD). The output of each countershould be double buffered. Two virtual backlight buffers 215 may be usedto store newly created backlight based on incoming image data andrescale the gain of outgoing LCD data.

The embodiment for the architecture described here would implement thesteps above using a “Pitch and Catch” approach. While one block is‘catching’ and analyzing the incoming video data, the other block isscaling and ‘pitching’ video data to the output. As shown in FIG. 13,the upper half of the system is in “catch” mode. During this phase,incoming RGB data is sampled by the histogram accumulators 210 whilebeing stored in the frame buffer 200. After 135 lines have beenbuffered, the contents of the twenty-four histogram accumulators 210 aremade available to the digital signal processor 220 (DSP). The DSP 220then calculates the brightness of each of the corresponding subsectionsand updates the virtual backlight buffer 215. This process is repeatedseven more times for the remaining video data. Note that the last eightsubsections placed into the virtual backlight may have to be calculatedduring the “vertical retrace” period.

The lower half of the system is operating in “pitch” mode. During thisphase, each pixel from the input buffer 200 is divided by thecorresponding pixel in the virtual backlight buffer 215 and sent to thevideo out MUX. To speed execution and avoid the use of a hardwaredivider, a lookup table may be used to determine a scaling factor. Thisfactor can then be used to rescale the RGB data with three 8×8multipliers. Concurrent with the rescaling operation, the individualsubsections of the backlight matrix will be updated synchronously usingthe values calculated during the “catch” phase.

It should be noted that the system and method described herein has beendescribed with reference to each ‘frame’ and in an exemplary embodimentthe backlight subsections would be updated for each ‘frame.’ However,there are many different frame rates of video which exist as well asdifferent refresh rates of LCD displays (ex. 60 Hz, 120 Hz, 240 Hz,etc.). As used herein, the term ‘frame’ represents each time that thepixel voltages are updated for the LCD display. Thus, the backlightsubsections should preferably be updated (and the LCD subpixel voltagesre-scaled) each time that a new set of subpixel data is sent to the LCDdisplay.

Having shown and described preferred embodiments, those skilled in theart will realize that many variations and modifications may be made toaffect the described embodiments and still be within the scope of theclaims. Thus, many of the elements indicated above may be altered orreplaced by different elements which will provide the same result andfall within the spirit of the claimed embodiments. It is the intention,therefore, to limit the invention only as indicated by the scope of theclaims.

What is claimed is:
 1. An LED backlit liquid crystal display (LCD)having individually controllable subsections of the LED backlight, theLCD comprising: an LED backlight having individually controllablesubsections; a dividing wall extending away from the LED backlight andseparating each adjacent subsection; a layer of liquid crystal materialplaced in front of the dividing walls; and a diffusing element placedbetween the dividing walls and the layer of liquid crystal material. 2.The LCD of claim 1 wherein: the height of the dividing walls is betweentwo and three inches.
 3. The LCD of claim 1 wherein: the distancebetween the dividing walls and the diffusing element is between 30 and40 mm.
 4. The LCD of claim 1 further comprising: a first and secondelectrical assembly in electrical communication with the liquid crystallayer and the LED backlight, where each electrical assembly comprises: ahistogram accumulator which accepts video input and prepares histogramdata; a frame buffer which accepts the video data; a digital signalprocessor which receives histogram data from the histogram accumulator,prepares virtual backlight data, and sends out controlling signals tothe liquid crystal layer and the LED backlight.
 5. The LCD of claim 4wherein: the first and second electrical assemblies operate in a pitchand catch mode.
 6. A system for controlling the interactions of lightbetween adjacent subsections of a dynamic LED backlight, the systemcomprising: a dividing wall positioned between each adjacent subsectionof the LED backlight.
 7. The system of claim 6 wherein: the dividingwall is adapted to produce a Gaussian relationship for the interactionsof light between adjacent subsections of the LED backlight.
 8. Thesystem of claim 6 wherein: the dividing wall is in contact with the LEDbacklight and extends away from the LED backlight.
 9. The system ofclaim 6 wherein: the dividing wall is sized and positioned so that halfof the light of each adjacent subsection is present at the location ofthe dividing wall.
 10. The system of claim 8 wherein: the dividing wallextends less than three inches away from the LED backlight.
 11. A systemfor controlling the interactions of light between adjacent subsectionsof a dynamic LED backlight, the system comprising: a first subsection ofthe LED backlight; a second subsection of the LED backlight positionedadjacent to the first subsection so as to create a border between thefirst and second LED subsections; and a dividing wall positioned alongthe border and extending away from the LED backlight.
 12. The system ofclaim 11 wherein: the dividing wall is adapted to allow approximatelyone-half of the luminance of the first subsection and approximatelyone-half of the luminance of the second subsection to be present at theborder.
 13. The system of claim 11 wherein: the luminance of the firstsubsection is reduced to approximately one-half of the full luminancewhen measured at the border.
 14. The system of claim 11 wherein: thefull luminance of the first subsection is not permitted to cross theborder into the second subsection.
 15. The system of claim 11 wherein:the luminance of the first subsection is gradually reduced as one movesfrom the border and into the second subsection.